A strange metal ball dropped out of the sky and slammed into the remote grassland of northern Namibia recently, according to press reports. The 14-inch-wide (35-centimeter) metallic sphere hit the ground about 480 miles (750 kilometers) north of Windhoek, the African country’s capital. It left a crater 13 inches (33 cm) deep and 12.5 feet (3.8 meters) across, the Agence-France Presse (AFP) reportedThursday.

The metal “space ball” weighs 13 pounds (6 kilograms). It has a rough surface and appears to consist of two halves that were welded together, according to AFP.

“It is not an explosive device, but rather hollow, but we had to investigate all this first,” police deputy inspector general Vilho Hifindaka told AFP.

However, Hifindaka and his colleagues still don’t know what the object is or where exactly it came from. They’ve contacted NASA and the European Space Agency for help, AFP reported. Locals apparently heard several small explosions a few days before the ball was found. Similar spheres have also been found in Australia and Central America over the last two decades, local authorities said.

Quite a bit of space junk has rained from the sky this year. In September, for example, NASA’s defunct Upper Atmosphere Research Satellite (UARS) — a 6.5-ton craft that monitored climate from 1991 until 2005 — plunged into the atmosphere over the Pacific Ocean.